This application is based upon Japanese Patent Application No. Hei. 11-257358 filed on Sep. 10, 1999, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a display panel driving system which has scanning electrodes and data electrodes and is driven by a sequential scanning method.
2. Related Art
As an example of an EL (Electro Luminescence) display panel for example, there is proposed a display panel comprising a structure constituted in such a manner that, on both sides of a light-emitting layer (EL layer), a plurality of scanning electrodes and a plurality of data electrodes are matrix-wise arranged, and the display picture elements formed at the positions at which the respective electrodes cross each other are made to emit light by line-sequential scanning. Such a display panel has the characteristic that, in proportion to the increase in number of the light-emitting picture elements on one and the same scanning electrode, the bluntness of the voltage waveform applied through the respective electrodes is enlarged. Due to this, there is caused the phenomenon (the so-called shadowing phenomenon) that the brightness of the picture elements which emit light during each scanning period comes to vary in accordance with the number of the light-emitting picture elements, as a result of which a brightness irregularity, (display unevenness) is caused, thus deteriorating the display quality. This is a problematic point.
In order to cope with such a problematic point, a technique as disclosed in Japanese Patent Publication No. 48137/1995 or the specification of Japanese Patent No. 2797185 has so far been proposed. According to this technique, in order to suppress the shadowing phenomenon, correction control is executed in such a manner that the light-emitting picture element number corresponding to one scanning period is counted by the use of a capacitor or digital type counter, and, on the basis of the counting result thus obtained, the pulse width of the scanning voltage applied to the scanning electrodes is changed.
In case of the above-mentioned known technique, the relationship between the light-emitting picture element number corresponding to one scanning period and the pulse width of the scanning voltage at the time of correction control is a linear proportional relationship. However, due to the fact that, in case of the EL display panel, the relationship between the light-emitting picture element number and the brightness varies in accordance with a change in the picture element arrangement (the scanning electrode number and the data electrode number), the picture element capacitance, etc., it becomes necessary to sequentially adjust the relationship between the light-emitting picture element number corresponding to one scanning period and the pulse width of the scanning voltage. Due to this, in case that the relationship between the light-emitting picture elements corresponding to one scanning period and the pulse width of the scanning voltage can be controlled only as a linear proportional relationship as according to the known technique, there is encountered the problem that, in case of some kind of display panel, it turns out to be difficult to suppress the occurrence of the shadowing phenomenon (that is, the occurrence of brightness irregularity). Further, there is the characteristic that, even in case of one and the same display panel, the relationship between the light-emitting picture element number and the brightness does not become a linear proportional relationship in case that the driving condition (such as, e.g., the pulse width of the scanning voltage) is changed. Due to this, in case of the known technique, it becomes difficult to accurately suppress the occurrence of the shadowing phenomenon, depending on the driving condition.
The present invention has been made in order to give a solution to the above-mentioned problem, and it is the object of the invention to provide a display panel driving system which can achieve effects such as the effect that the occurrence of a display irregularity on the display panel can be accurately suppressed without regard of the characteristic of the display panel and the driving condition.
According to the first aspect of the present invention, a control circuit applies the composite voltage consisting of a scanning voltage and a data voltage to the display panel by a sequential scanning method to thereby turn into a display state the display elements formed in the regions in which scanning electrodes and data electrodes are opposed to each other. At this point of time, in the control circuit, a counter means comes to count the number of those display elements which are brought into a display state in response to the application of a voltage corresponding to one scan, and, by the counting result thus obtained, an address of data maps in a memory means is designated. Further, a signal generation means comes to generate a control signal for controlling the application time of the above-mentioned composite voltage so as to assume a state associated with the pulse width data or voltage value data corresponding to the designated address.
Into the above-mentioned data maps, a plurality of addresses corresponding to the counting ranges of the counter means and a plurality of stages of pulse width data indicating the pulse width of the composite voltage or a plurality of stages of voltage value data indicative of the magnitude of the composite voltage are previously written in the state in which they are associated with each other; and therefore, it becomes possible to execute the correction control of changing the application time or the magnitude of the composite voltage (that is, the display state of the display elements) on the basis of the counting result (in other words, the number of those display elements which are brought into a display state in response to one scan) of the counter means. Thus, the occurrence of a shadowing phenomenon can be suppressed. In this case, the relationship of correspondence between the addresses in the data maps and the pulse width data or the relationship of correspondence between the above-mentioned addresses and the voltage value data come to be settable into an optimum state corresponding to the characteristic and the driving condition of the display panel which is the object to be driven. More specifically, in case of the known technique, the relationship between the number of those display elements which are brought into a display state during one scanning period and the application time of the composite voltage can be controlled only as a linear proportional relationship, whereas, according to the present invention, the relationship between the above-mentioned display element number and the application time or magnitude of the composite voltage can be controlled in to an arbitrary state. Accordingly, the application time or magnitude of the composite voltage controlled by the control signal outputted from the signal generation means can be controlled into an optimum state taking into consideration the characteristic and the driving condition of the display panel, so that the occurrence of a display irregularity on the display panel can be accurately suppressed without regard to the characteristic and driving condition of the display panel.
In the second aspect of the present invention, likewise, the display elements are turned into a display state by the control circuit in response to applying to the display panel the composite voltage by the sequential scanning method, the above-mentioned composite voltage consisting of the scanning voltage and the data voltage. At this point of time, in the control circuit, the counter means comes to count the number of those display elements which are brought into a display state in response to the application of a voltage corresponding to one scan, and, by the ensuing counting result, an address in the data maps in the memory means is designated. Further, a shift register converts the pulse width data or the voltage value data corresponding to the designated address into a serial signal train synchronized with a clock signal and, at the same time, a signal processing circuit produces a control signal, on the basis of the output from the shift register, for controlling the application time or magnitude of the composite voltage so as to assume a state corresponding to the above-mentioned read pulse width data or voltage value data.
In the above-mentioned data maps, data similar to the data in case of the first aspect of the invention are written. Accordingly, in this second aspect of the invention, likewise, the correction control of changing the application time of the composite voltage on the basis of the counting result of the counter means can be executed, so that the occurrence of a shadowing phenomenon can be suppressed. Further, the application time or magnitude of composite voltage controlled by the control signal from the signal processing circuit can be controlled into an optimum state with the characteristic and driving condition of the display panel taken into consideration, and thus, the occurrence of a display irregularity on the display panel can be accurately suppressed without regard to the characteristic or the driving condition of the display panel.